"He has been missing for four days now, and as yet I have had no contact from any official agency advising me as to the progress of the search.

"At this stage I feel it is essential that the search be intensified as time is running out for Gareth, so I would really appreciate the support of the Malaysian authorities and the UK government with this."

She added that she and Mr Huntley's father planned to fly out tomorrow to help in the search.

Mr Huntley had been working at the Jura Turtle Project. Fellow volunteer Charles Fisher said a group went to search for him after he did not return from the "huge wilderness".

He said they checked various different routes to the waterfall 6km away that he might have taken, while a further search the next day also proved fruitless.

Mr Fisher added: "Then the afternoon of the second day the police were informed - they sent a couple of members of the police force along to have a look but didn't go far or look very much - they were just sort of assessing the situation.

"Then the next day, the 29th, a group of volunteers went out and looked then came back again. Another group from the local community also went out as well and went deep into the jungle. The police were no longer physically looking at that point - I think they were arranging for a search party but nothing happened that day.

"Then today we've just been hoping the state police will do a proper search but nothing has happened yet. I don't know what's going on.

"It's a huge wilderness out there - a remote location. He could have taken a wrong turn and just got lost in another valley - we just don't know. The trouble is the police probably don't have proper search equipment - they need extra support."

A Facebook group has been set up to raise awareness about Mr Huntley's disappearance.

A spokeswoman for the Foreign Office said: "We are aware that a British national has been reported missing in Malaysia since 27 May.

"We are providing consular assistance to the family and are liaising closely with the local authorities."